To identify factors regulating initiation of follicle growth in primates the ovarian cycle of sexually mature rhesus monkeys was interrupted by surgical ablation of the preovulatory follicle and functioning corpus luteum. Monitoring of circulating levels of gonadotropins and ovarian steroids (estrogens and progesterone), as well as gross ovarian morphology indicates that the time and site of new follicle growth in the rhesus monkey are not random events; rather, they appear to be influenced locally by the dominant follicle or active corpus luteum. The objectives of the present study are aimed at interrelating the activities of the follicle and corpus luteum, along with pituitary gonadotropins, that contribute to the cyclic development of mature follicles in the primate. These studies can be related to problems of human female infertility (e.g. anovulation and short luteal phase) and pharmacologic control of fertility.